Generally, this kind of front derailleur, as disclosed in Japanese Utility Model Publication Gazette No. Sho 57-39,271, is provided with a linkage mechanism comprising a fixing member fixed to a seat tube of the bicycle frame, a pair of first and second linkage members connected to the fixing member through a pair of pivot shafts, and a movable member having a chain guide and connected to free ends of the linkage members through a pair of pivot shafts. The first linkage member is provided at its root portion with an integral operating arm for supporting a control wire, so that the control wire is operated to deform the linkage mechanism so as to move the chain guide axially of the multistage front chain gear assembly.
In the above-described construction, since the first linkage member is provided with the operating arm subjected to an operating force of the control wire, the pivot shaft for pivotally supporting the first linkage member to the fixing member is fully subjected to the operating force of the control wire. Therefore, as disclosed in Japanese Utility Model Publication Gezette No. Sho 57-39,271, at a pivot portion of the first linkage member to the pivot shaft are provided a recess and a pair of mounting members having through bores, with the operating arm being integral with one of the mounting members. At the fixing member is provided a projecting mounting base to be fitted into the recess, so that the mounting base is fitted into the recess and the pivot shaft is fitted into the through bores and supported at an intermediate portion to the fixing member. Also, the mounting members at the first linkage member are supported to both ends of the pivot shaft to form a double end support construction is capable of withstanding a heavy load.
In such conventional construction, however, it is necessary to particularly form by cutting-processing the recess at the first linkage member and the mounting base at the fixing member, thereby creating a problem in that the processing is complicated resulting in high manufacturing costs. Since the operating arm is integral with one mounting member, the mounting member must be larger in thickness to increase its strength, thereby giving a poor appearance to that extent.
In order to pivotally support the first linkage member having the operating arm to the fixing member through the pivot shaft, it is considered that, for example, the pivot shaft is fixed at one axial end to the fixing member and pivotally supports the first linkage member. In this case, since the first linkage member is supported to the pivot shaft of cantilever construction, the pivot shaft is required to be larger in diameter from the viewpoint of strength, whereby a base of the first linkage member and the pivot shaft fixing portion at the fixing member are large in size to result in an unbalanced design for the entire derailleur.